Conventionally, this kind of vaporizer has an arrangement wherein a gas-liquid mixture comprising a liquid precursor and a carrier gas used for forming a film is discharged from a nozzle so as to be depressurized, and then heat is applied by a heating channel arranged on a downstream side of the nozzle so as to vaporize the liquid precursor (patent document 1).
However, some liquid material, that is often used as a precursor for high-k process, of a recent semiconductor element has a property of being easy to be thermally decomposed and has low vapor pressure. As a result, the following problem is generated more than ever before.
More specifically, the liquid precursor has to be at a high temperature in order to be vaporized because it has a low vapor pressure. However, since the liquid precursor is easy to be thermally decomposed, if exposed to high temperature in order to vaporize, a part of the precursor is deteriorated so as to be a residue. As a result, the nozzle might be clogged or a particle might be produced.
Furthermore, since a conventional vaporizer is of a single nozzle structure, if a nozzle is clogged, there would be a problem in that it becomes impossible to continue vaporization, and operation is halted almost completely. Especially in a semiconductor manufacturing process, it is not preferable to halt the operation.
In considering this problem, if a plurality of nozzles are simply arranged, the mist sprayed from each of the nozzles overlap with each other to be mixed at some position so as to generate a difference in the concentration of the mist. Thus, there is no other choice but for the mist to be vaporized at a temperature adjusted for the highest concentration. As a result, thermal decomposition of the precursor is likely to be caused.
A slightly improved version of the vaporizer is shown in FIG. 14. The arrangement in FIG. 14 contains a description of a structure wherein a plurality of heating channels are arranged to correspond to a plurality of nozzles, however, the heating channel and the nozzle are discontinuous and a space is formed therebetween. Thus the same problem as that mentioned above will be generated, more or less, because there will be a difference in the concentration of the spray due to a difference in a degree of overlap of the spray.    Patent document 1: Japan patent laid-open number 2003-163168